$('document').ready(
        function()
        {
            $('#contact_form').submit(
                function()
                {
                    //init
                    var error = false;
                    
                    //get data
                    var fullName = $('#full_name').val();
                    var telNo    = $('#tel').val();
                    var email    = $('#email_address').val();
                    var comments = $('#your_comments').val();
                   
                    //full name is required
                    if( fullName.length == 0 )
                    {
                        $('#full_name').addClass('missing');
                        error = true;
                    }
                    else
                    {
                        $('#full_name').removeClass('missing');
                    }
                    
                    //tel no is required
                    if( telNo.length == 0 )
                    {
                        $('#tel').addClass('missing');
                        error = true;
                    }
                    else
                    {
                        $('#tel').removeClass('missing');
                    }
                    
                    //email is required
                    if( email.length == 0 )
                    {
                        $('#email_address').addClass('missing');
                        error = true;
                    }
                    else
                    {
                        $('#email_address').removeClass('missing');
                    }
                    
                    //comments are required
                    if( comments.length == 0 )
                    {
                        $('#your_comments').addClass('missing');
                        error = true;
                    }
                    else
                    {
                        $('#your_comments').removeClass('missing');
                    }
                   
                    //has an error occurred?
                    if( error )
                    {
                        return false;
                    }
                    else
                    {
                        return true;
                    }
                }
            );
        }
    );